As indicated in U.S. Pat. No. 3,854,943, in a typical monochromatic manifold imaging system, an imageable member is prepared by coating a layer of a cohesively weak photoresponsive imaging material onto a substrate. This coated substrate is called the "donor". In preparation for the imaging operation, the imaging layer is activated, as by treating it with a swelling agent or partial solvent for the material. This step may be eliminated if the layer retains sufficient residual solvent after having been coated on the substrate from a solution or paste. The activating step provides the dual function of making the top surface of the imaging layer slightly tacky and, at the same time, weakening the imaging layer structurally so that it can be fractured more easily along a sharp line which defines the image to be reproduced. Once the imaging layer is activated, a receiving sheet is laid down over its surface. An electrical potential is then applied across this manifold set while it is exposed to a pattern of light-and-shadow representative of the image to be reproduced. Upon separation of the donor substrate and the receiving sheet, the imaging layer fractures along the lines defined by the pattern of light-and-shadow to which it has been exposed, with part of this layer being transferred to the receiving sheet while the remainder is retained on the donor sheet. Thus, a positive image is produced on one while a negative image is produced on the other. The system is capable of producing monochromatic images of excellent density and resolution. If an attempt is made to uniformly mix pigment particles responding to different colors throughout the imaging material, in some embodiments color reproductions may not be entirely satisfactory since particles of different colors scattered throughout the thickness of the imaging layer may tend to mask each other and prevent stripping of single colors only in desired single colored areas.
To achieve color separation in a single set imaging system, said U.S. Pat. No. 3,854,943 provides a subtractive imaging mono-layer, sandwiched between donor and receiver members, which is comprised of a plurality of randomly mixed agglomerates of at least two different colors which respond selectively to light. The randomly mixed agglomerates in an electric field respond to radiation within their sensitivities by selectively adhering to the receiver during sandwich separation whereupon each individual agglomerate is easily and independently removed from the imaging layer. While images resulting from this system demonstrate excellent color separation, it is largely confined to the use of pigment agglomerates. The nature of the colors in such a system depends entirely on the brilliancy of the individual pigments. Such systems generally result in low color saturation because of the particulate nature of the color entities.
In U.S. Pat. No. 4,172,721, there is provided an imaging method utilizing an imaging monolayer of composite particles. Those particles comprise a small resin particle containing an electrically photosensitive pigment and a solid form or particulate dye material. The monolayer is then subjected to an electric field, exposed to an image pattern of sensitizing electromagnetic radiation, and the image is formed upon separation of the photosensitized composite particles from the unsensitized composite particles, and the dyes of an image are imbibed into a substrate material to color-amplify the image. While that method provides a dense, brilliant, polychromatic, well-fixed dye image in a substrate, the photosensitivity of the "driver" materials in the composite particles is not as spectrally selective as it is sometimes desired.
Accordingly, there is a need for an improved method and materials for imaging using a monolayer of electrically photosensitive particles.
It is, therefore, an object of the invention to provide an imaging method and materials overcoming the above-indicated deficiencies.
It is another object of the present invention to provide a polychromatic imaging system utilizing an imaging mono-layer which is capable of reproducing accurately and vividly a polychromatic original.